function U = upsilon(q, param)

    sigma = param.sigma;
    epsilon = param.epsilon;
        
   U =  q.^((sigma-1)/sigma);%1 + (sigma-1)*exp(1/epsilon)*epsilon^(sigma/epsilon-1)*...
        %(uigamma(sigma/epsilon,1/epsilon) - ...
        %uigamma(sigma/epsilon, (q.^(epsilon/sigma))/epsilon));
    
end